(i) Field of the Invention
The present invention relates to a method for forming a coating film, and more specifically it relates to a method for forming a coating film which is desirable to coat relatively flexible plastic materials such as RIM (Reaction Injection Molding), ABS, polyurethane, polypropylene and polycarbonate for bodies and bumpers of automobiles and which is excellent in water repellency, stain resistance, bending resistance at low temperatures, and gloss maintenance and stain resistance when exposed outdoors.
(ii) Description of the Prior Art
In recent years, in reply to needs such as variegation of designs, decrease of weight and improvement of impact resistance of automobiles, plastics and elastomers are often used for bumpers, fenders, spoilers, wheels and the like of the automobiles. On these surfaces of flexible plastic materials, there are used coating materials for forming similarly flexible coating films. Particularly, in the case of the coating material which is applied onto the bumper, it is necessary that the coating film of the coating material is flexible enough to absorb deforming stress, instantaneous impact force and the like applied at a low temperature of from -10.degree. C. to -40.degree. C. and to thereby prevent the coating film from cracking.
Heretofore, as the coating materials for the members made from plastics and elastomers, there are known an acrylic urethane (Japanese Laid-open Patent Publication No. 61-93870) and a polyester urethane coating material (Japanese Laid-open Patent Publication No. 61-26614). In addition, Japanese Laid-open Patent Publication No. 58-32662 discloses an acrylic urethane coating material in which a polycaprolactone polyol is used in order to improve the flexibility of the urethane coating material. The coating films made from these urethane coating materials usually have excellent performance at low temperatures, but since they are soft, sand grains, dust, soot, metallic powder and the like tend to adhere to the surfaces thereof. Therefore, when an outdoor exposure test is carried out, the appearance of the coating films noticeably deteriorates with time inconveniently.